You see this question from the point of view of a well informed purchaser and I do not doubt that the contributors to this forum are all knowledgeable purchasers. However, a very large proportion of those who buy DSLRs are not by any means enthusiasts. They do not read reviews and look into the depth of the systems offered by the various manufacturers before deciding what to buy. They buy an entry level or possibly superior DSLR with kit lens and never buy another lens or accessory.

Whilst the Canon and Nikon systems have the advantages that you describe, the vast proportion of buyers are not interested in those aspects and are most likely not even aware of them. They see more Canon and Nikon cameras than other makes and are generally aware that those are the cameras used by professionals.

I have lived for over thirty years in tourist destinations and see hordes of these camera users every day. They are the "sheep" who buy according to the brand recognition that others have mentioned.